NEW YORK - Six different types of prescription drugs were found in Heath Ledger's apartment - including anti-anxiety medications and sleeping pills - though the cause of his death won't be known for several days after a preliminary autopsy Wednesday was inconclusive, authorities said.

A rolled-up $20 bill was also found on the floor near the Australian actor's bed, but lab tests detected no traces of drug residue. Police also said no illegal drugs were found in the apartment.

Among the prescription medications found were pills to treat insomnia and anxiety, and an antihistamine, according to two law enforcement officials who spoke on condition of anonymity because the investigation is ongoing. Three of the drugs were prescribed in Europe, the sources said.

The $20 bill was found on the floor neare Ledger's bed, NYPD spokesman Paul Browne said lab tests found nothing to indicate it had been used to snort drugs.

The Australian-born actor was found dead Tuesday by his housekeeper and a massage therapist - lying naked and face-down on his bed, police said. The pills were found in bottles in Ledger's bedroom and bathroom, and police said the death was caused by a possible drug overdose and appeared to be accidental.

Ellen Borakove, a spokeswoman for the medical examiner's office, said the autopsy on the 28-year-old actor was inconclusive and that more would be known in about 10 days, when more tests were completed.

News of the death stunned family, fans and colleagues.

'Working with Heath was one of the purest joys of my life,' said Ang Lee, who directed Ledger in 'Brokeback Mountain.' 'He brought to the role of Ennis more than any of us could have imagined - a thirst for life, for love and for truth, and a vulnerability that made everyone who knew him love him. His death is heartbreaking.'

Lee Daniels, who produced the critically acclaimed 'Monster's Ball' in which Ledger starred, strongly disputed any notion that Ledger had a drug problem.